A method for treating waste waters to remove oils and/or COD therefrom, which comprises accomodating solid porous packing pieces and activated carbon particles in a container, the porous packing pieces forming a stationary porous packed bed, the average pore diameter of the porous packing pieces being 1.5 to 8 times the average diameter of the activated carbon particles; introducing a waste water, if desired, together with an oxygen-containing gas and/or an oxidizing gas, from the bottom portion of the container to fluidize the activated carbon particles within the pores of the porous packing pieces and in spaces among the adjoining porous packing pieces and simultaneously to contact the waste water with the activated carbon particles; maintaining the upper level of the fluidized bed of the activated carbon particles at least 5 cm below the upper level of the porous packed bed; and withdrawing the waste water which has been so contacted from the top portion of the container.